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TUNEFS(8) FreeBSD System Manager's Manual TUNEFS(8)
NAMEtunefs -- tune up an existing UFS file system
SYNOPSIStunefs [-A] [-aenable | disable] [-emaxbpg] [-favgfilesize]
[-jenable | disable] [-Jenable | disable]
[-kheld-for-metadata-blocks] [-Lvolname] [-lenable | disable]
[-mminfree] [-Nenable | disable] [-nenable | disable]
[-ospace | time] [-p] [-savgfpdir] [-Ssize]
[-tenable | disable] special | filesystemDESCRIPTION
The tunefs utility is designed to change the dynamic parameters of a UFS
file system which affect the layout policies. The tunefs utility cannot
be run on an active file system. To change an active file system, it
must be downgraded to read-only or unmounted.
The parameters which are to be changed are indicated by the flags given
below:
-A The file system has several backups of the super-block. Specify-
ing this option will cause all backups to be modified as well as
the primary super-block. This is potentially dangerous - use
with caution.
-aenable | disable
Turn on/off the administrative POSIX.1e ACL enable flag.
-emaxbpg
Indicate the maximum number of blocks any single file can allo-
cate out of a cylinder group before it is forced to begin allo-
cating blocks from another cylinder group. Typically this value
is set to about one quarter of the total blocks in a cylinder
group. The intent is to prevent any single file from using up
all the blocks in a single cylinder group, thus degrading access
times for all files subsequently allocated in that cylinder
group. The effect of this limit is to cause big files to do long
seeks more frequently than if they were allowed to allocate all
the blocks in a cylinder group before seeking elsewhere. For
file systems with exclusively large files, this parameter should
be set higher.
-favgfilesize
Specify the expected average file size.
-jenable | disable
Turn on/off soft updates journaling.
-Jenable | disable
Turn on/off gjournal flag.
-kheld-for-metadata-blocks
Set the amount of space to be held for metadata blocks. When
set, the file system preference routines will try to save the
specified amount of space immediately following the inode blocks
in each cylinder group for use by metadata blocks. Clustering
the metadata blocks speeds up random file access and decreases
the running time of fsck(8). While this option can be set at any
time, it is most effective if set before any data is loaded into
the file system. By default newfs(8) sets it to half of the
space reserved to minfree.
-Lvolname
Add/modify an optional file system volume label.
-lenable | disable
Turn on/off MAC multilabel flag.
-mminfree
Specify the percentage of space held back from normal users; the
minimum free space threshold. The default value used is 8%.
Note that lowering the threshold can adversely affect perfor-
mance:
+o Settings of 5% and less force space optimization to always be
used which will greatly increase the overhead for file
writes.
+o The file system's ability to avoid fragmentation will be
reduced when the total free space, including the reserve,
drops below 15%. As free space approaches zero, throughput
can degrade by up to a factor of three over the performance
obtained at a 10% threshold.
If the value is raised above the current usage level, users will
be unable to allocate files until enough files have been deleted
to get under the higher threshold.
-Nenable | disable
Turn on/off the administrative NFSv4 ACL enable flag.
-nenable | disable
Turn on/off soft updates.
-ospace | time
The file system can either try to minimize the time spent allo-
cating blocks, or it can attempt to minimize the space fragmenta-
tion on the disk. Optimization for space has much higher over-
head for file writes. The kernel normally changes the preference
automatically as the percent fragmentation changes on the file
system.
-p Show a summary of what the current tunable settings are on the
selected file system. More detailed information can be obtained
from the dumpfs(8) utility.
-savgfpdir
Specify the expected number of files per directory.
-Ssize
Specify the softdep journal size in bytes. The minimum is 4M.
-tenable | disable
Turn on/off the TRIM enable flag. If enabled, and if the under-
lying device supports the BIO_DELETE command, the file system
will send a delete request to the underlying device for each
freed block. The trim enable flag is typically set when the
underlying device uses flash-memory as the device can use the
delete command to pre-zero or at least avoid copying blocks that
have been deleted.
Note that this does not trim blocks that are already free. See
the fsck_ffs(8)-E flag.
At least one of these flags is required.
FILES
/etc/fstab read this to determine the device file for a specified mount
point.
SEE ALSOfs(5), dumpfs(8), gjournal(8), growfs(8), newfs(8)
M. McKusick, W. Joy, S. Leffler, and R. Fabry, "A Fast File System for
UNIX", ACMTransactionsonComputerSystems2, 3, pp 181-197, August
1984, (reprinted in the BSD System Manager's Manual, SMM:5).
HISTORY
The tunefs utility appeared in 4.2BSD.
BUGS
This utility does not work on active file systems. To change the root
file system, the system must be rebooted after the file system is tuned.
You can tune a file system, but you cannot tune a fish.
FreeBSD Ports 11.2 April 19, 2016 FreeBSD Ports 11.2